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 Table of Contents  
Year : 2022  |  Volume : 34  |  Issue : 4  |  Page : 447-451

In Vitro study of the effect of conservative endodontic cavities on fracture strength in mandibular molars using CBCT analysis

1 Department of Conservative Dentistry and Endodontics, Government Dental College and Hospital, Afzalgunj, HyderabadA, Telangana, India
2 Department of Conservative Dentistry and Endodontics, Kamineni Institute of Dental Sciences, Sreepuram, Narketpally, Nalgonda, Telangana, India
3 Department of Periodontics, Kamineni Institute of Dental Sciences, Sreepuram, Narketpally, Nalgonda, Telangana, India

Date of Submission12-Apr-2022
Date of Decision15-Nov-2022
Date of Acceptance16-Nov-2022
Date of Web Publication09-Dec-2022

Correspondence Address:
Uppalapati Vishwaja
Department of Conservative Dentistry and Endodontics, Government Dental College and Hospital, Afzalgunj, 500012, Hyderabad, Telangana
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jiaomr.jiaomr_127_22

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Background: Endodontically treated teeth with conservative cavity preparation show better fracture resistance than traditional designs. Objective: To compare the fracture strength of endodontically treated teeth using traditional endodontic cavity (TEC), conservative endodontic cavity (CEC), truss access cavity (DDC), and ninja endodontic cavity (NEC) access designs. Methods: In an in-vitro study, 50 freshly extracted human intact mandibular molars with two separate roots were selected. The anatomic crown height, buccolingual, and mesiodistal dimensions were measured and randomized to control (intact teeth), TEC, CEC, DDC, and NEC groups (n = 10). Using cone-beam computed tomography, TEC, CEC, DDC, and NEC access cavity outlines were planned. Following endodontic treatment, the fracture strength of teeth was assessed using a universal testing machine and fracture type with a stereomicroscope. Results: The mean volume percentage of the coronal hard tissue removal was significantly lower in the NEC group than in the TEC, and CEC groups (P < 0.05), while the difference was comparable between the NEC and DDC groups (P > 0.05). The fracture strength of teeth prepared with the TEC design was significantly lower than teeth prepared by CEC, DDC, NEC, and control groups (P < 0.05). Conclusion: Teeth with traditional access preparation showed lower fracture strength than the conservative approaches.

Keywords: Access cavity, cone beam computed tomography, conservative endodontic cavity, fracture strength
Key Message: CBCT is one of the valuable aids in determining the effect of access cavities fracture strength of the tooth.

How to cite this article:
Vishwaja U, Surakanti JR, Vemisetty H, Guntakandla VR, Bingi SK, Vantari SR. In Vitro study of the effect of conservative endodontic cavities on fracture strength in mandibular molars using CBCT analysis. J Indian Acad Oral Med Radiol 2022;34:447-51

How to cite this URL:
Vishwaja U, Surakanti JR, Vemisetty H, Guntakandla VR, Bingi SK, Vantari SR. In Vitro study of the effect of conservative endodontic cavities on fracture strength in mandibular molars using CBCT analysis. J Indian Acad Oral Med Radiol [serial online] 2022 [cited 2023 Feb 3];34:447-51. Available from: http://www.jiaomr.in/text.asp?2022/34/4/447/363012

   Introduction Top

The current endodontic practice prioritizes minimal tooth preparation and maximum natural tooth preservation. Access cavity preparation is the first and important step in endodontics that determines good instrumentation and effective cleaning during the endodontic procedure. Hence, a successful and quality endodontic treatment is dependent on a good access cavity design.[1] The additional extension for prevention to the straight-line access cavity design of the TEC is associated with the loss of crucial dentin, thereby weakening the tooth structure and leading to fracture.[2]

To overcome this problem, conservative endodontic access cavity (CEC) designs were introduced to preserve the roof of the pulp chamber and peri cervical dentin.[3] CEC techniques have revolutionized the treatment approach by shifting the rationale from operator-centric to tooth-centric cavity preparations. Among the different CEC designs, Clark and Khademi (2010)[4] proposed contracted endodontic access cavity design, whereas Auswin and Ramesh (2017)[5] proposed the Truss access cavity or orifice-directed dentin conservation (DDC) access design. In this design, cavity preparation and dentin removal right above the orifice allow the preservation of maximum coronal tooth structure. The most recent Ninja endodontic access cavity (NEC) designs with their ultraconservative approach have shown better fracture resistance than a traditional cavity.[6]

CBCT has great potential to become a valuable tool for diagnosing and managing endodontic problems and assessing root fractures, apical periodontitis, resorptions, perforations, root canal anatomy, and the nature of the alveolar bone topography around teeth. A cautious and rational approach is advised when considering the use of CBCT imaging in endodontics. In addition to the advanced endodontic techniques, Cone-Beam Computed Tomography (CBCT) helps localize the canal orifice and canal direction.[7]

CBCT provides three-dimensional visualization of the tooth anatomy along with location, the shape of the orifices, the number of canals, and the pathologies associated with it. This localization of canals eases the clinical procedure and allows a conservative approach by minimizing additional tooth preparations.[8] Analysis of images before and after cleaning and shaping allows accurate measurements of root canal morphology, the volume of dentin removed, remaining dentin thickness, transportation of canal pathways, and importantly, the canal wall surface area contacted and untouched by the instruments, thereby improving the fracture strength.[9]

The present experimental study was conducted to comparatively evaluate the fracture strength of different endodontically treated extracted mandibular molar teeth using TEC, CEC, DDC, and NEC access cavities.

   Material and Methods Top

Ethical clearance was obtained before the study (Ref. Number: KIDS/IEC/2018/01). A total of 50 freshly extracted human mandibular molars teeth due to periodontal reasons with completely formed apices having similar coronal dimensions and root lengths were selected. Teeth with caries, deformities, cracks, fractures, restorations, and curved roots. pulp/root canal calcifications, pulp stones, and root resorptions were excluded after the radiographic screening. To prevent dehydration of extracted teeth, we used 0.1% thymol solution to store teeth. The study design is outlined in [Figure 1].
Figure 1: Study design

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All teeth in the test groups were mounted in a wax base. To minimize excess cavity preparation, an outline of access cavities was prepared by projecting trajectories to each canal orifice using CBCT imaging. All preparations were done using a surgical operating microscope with enhanced vision (16X magnification). Access cavities were prepared using Endo access bur, Endo Z bur attached to a handpiece of speed 10000 rpm for TEC, and size 856 diamond burs for other conservative test groups. Following this, prepared teeth were scanned again using CBCT and the images were imported to the MeVisLab image processing and visualization platform for 3-dimensional representation of the teeth and segmentation of access preparations. Further, we calculated the volume percentage loss of coronal enamel and dentin during access cavity preparation. Root canal preparation, instrumentation, shaping of canals, and canal disinfection were done as per standard protocol.[1],[6],[10] The prepared canals were filled with size 25 gutta-percha cone, sealed with the resin-based endodontic sealer, and confirmed using postoperative radiographs. The direct composite was used to seal the access cavity preparations [Figure 2].
Figure 2: Radiographs of traditional, conservative, truss, and ninja access cavities, Access cavities, and Radiographs of teeth after complete obturation

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To test the fracture strength, all teeth in test and control groups were mounted on Aluminium rectangular molds and filled with self-curing resin up to 2 mm apical to the cementoenamel junction. The teeth were subjected to 480 thermal cycles with temperatures between 5°C and 55°C and placed in a water bath. Fracture strength was tested using Instron Universal Testing Machine ahead. Compressive force (0.5 mm/min crosshead speed) was directed at the central 6 mm diameter steel compressive fossa at 30° angles to the long axis to simulate functional masticatory forces. The compressive forces were measured in Newtons and the highest load-causing fracture was recorded. Using a stereomicroscope, we examined the fractured specimens and classified them into different fracture types, and fracture levels were assessed. Fractures above the acrylic resin were classified as “restorable,” while those below the acrylic level were considered “unrestorable.”

Statistical analysis

All collected data were entered into Microsoft Excel and imported to SPSS software (version 21) for statistical analysis. Data were summarized descriptively as mean, standard deviation, frequency, and percentages. We used the Kolmogorov-Smirnov test to test the normality of data and the Levene test for homogeneity of variances. Since our data had a non-normal distribution, nonparametric tests including One Way Analysis of Variance and the Bonferroni Post Hoc test were applied. P values < 0.05 were considered statistically significant.

   Results Top

The mean of buccolingual, mesiodistal dimension, and anatomic crown height was comparable between groups (p > 0.05) [Table 1]. Volume percentage loss of tooth structure was highest in the TEC group (52%) and least in the NEC group (13%). The volume percentage loss of enamel and dentin between DDC and NEC was comparable (p = 0.177) [Table 2].
Table 1: Baseline teeth dimensions of all teeth specimen

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Table 2: Multiple comparisons of volume percentage of the coronal enamel and dentin removed in the tested group

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We observed mesiodistal fractures in all teeth with varying apical extent. The mean load at fracture for teeth in the TEC group was significantly lower than in the control and NEC groups. Fractures were categorized into restorable and unrestorable fractures [Figure 3]. With stereomicroscope analysis, while the frequency of the restorable fractures was significantly higher in the control group than the unrestorable fractures (7 vs 3; P < 0.05), the frequency of unrestorable fractures was higher in the TEC (8 vs 2), CEC (8 vs 2), DDC (6 vs 4) and NEC (7 vs 3) groups than restorable fractures (p < 0.05). However, intergroup comparisons between groups were not statistically significant (p > 0.05).
Figure 3: Type of fracture assessed using stereomicroscope after the static test using Instron universal testing machine

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   Discussion Top

We comparatively evaluated the fracture strength of endodontically treated teeth using TEC, CEC, DDC, and NEC techniques. The percentage loss of tooth during access preparation was highest with traditional design and lowest in NEC designs. Loss of tooth structure, more specifically the dentin loss during the access cavity preparation steps is the main cause of fractures in root canal-filled teeth.[11],[12],[13] Theoretically it is perceived that minimal access cavity designs increase mechanical stability and fracture resistance of root-filled teeth.[3],[4],[14]

Since previous studies have reported no difference in TEC and CEC fracture strength in anterior teeth,[15] we selected mandibular molars as they are more susceptible to fracture secondary to masticatory forces.[16] With its three-dimensional volume rendering, CBCT is an excellent choice during the pre-planning of root canal treatment in recent years. It aids in the identification of all the canals and outlines the cavities before tooth preparations, especially in conservative approaches.[9]

Post access cavity, we measured the volume loss of coronal enamel and dentin removed by voxel counting and volume ratios and calculated the percentage difference. The Mean (SD) volume percentage loss of coronal enamel and dentin in the TEC group was [16.33 (1.46)] significantly higher than other groups, while the volume percentage between DDC and NEC was not statistically significant [4.80 (0.62) vs 4.25 (0.043)]. The results are by Plotino et al.[6] who reported significantly lower volume loss in NEC groups. Similarly, the percentage of volume loss of tooth structure observed was highest in the TEC group (52%) and least in the NEC group (13%), which is much higher than the 15% and 6% reported by Segarra et al.[17] The maximum tooth loss incurred in the TEC group could be due to maximum tooth preparation including unroofing of the pulp chamber to get straight-line access to root canals.[3],[6],[11] in the conservative designs, partial unroofing, preparation of separate cavities, and non-beveling of cavities resulted in less tooth structure loss.[6],[18]

Following the endodontic procedure, we restored the access cavities with bonded resin composite to simulate functional restorations in the oral cavity.[16] The previous study has suggested improved fracture resistance by up to 72% in access cavity-restored teeth.[19] While Bassir et al.[20] reported improved fracture resistance with adhesive restorations that improve fracture resistance than traditional restorative materials; Pradeep et al.[21] did not report any significant difference in the fracture strength of restored endodontically treated teeth using amalgam or composite resin. During the testing of fracture resistance with a universal mechanical testing machine,[15],[21] we standardized the procedure by using the same loading force to all teeth and applied compressive force with an angle to simulate the clinical setting.

Similar to Pradeep et al.[21] fracture strength of intact natural teeth (2428.75[952.92)) was significantly higher than test groups. While Plotino et al.[6] and Krishan et al.[15] reported lower fracture resistance in TEC than in conservative approaches. Similarly, Özyürek et al.[12] did not notice a difference between the fracture strength of TEC and CEC-treated teeth with class II cavities. Preservation of peri cervical dentin has shown increased fracture resistance in teeth prepared with the CEC technique.

Although, some previous studies have not shown improved fracture resistance in maxillary molars with CEC designs.[16] The improved fracture strength with conservative access cavity designs including CEC, DDC, and NEC in our study is mainly attributed to dentin preservation and smaller cavity preparations. The difference in study results could be related to variable study design, the technique used, the type of instrumentation, restorations, and the method of testing fracture resistance. Unfortunately, with CEC designs it is difficult to achieve good canal instrumentation and disinfection of some distal canals. Therefore, CBCT imaging and the use of surgical microscopes aid in minimizing the risk of missing canals and associated infections.

While traditional access cavity preparations increase the risk of microcracks resulting in decreased fracture strength of teeth, conservation of peri cervical tooth structure in conservative designs minimizes the risk of micro factors near the access cavity thereby increasing the fracture strength. Soffit seen in conservative cavities aids in improving the strength of the tooth.

The fractured specimens were categorized into “restorable” and “unrestorable” depending on the level of fractures. Similar to Plotino et al.[6] incidence of restorable fracture was higher in the control group and unrestorable fractures were higher in endodontically treated teeth. The samples under CEC, DDC, and NEC groups showed mesiodistal fractures while the samples under the TEC group showed a cuspal chipping pattern.

Despite the strengths of our study, the small sample size is one of the limitations. Secondly, although the loading pressure was given at an angle, however, the complex chewing process cannot be truly reflected in an in-vitro setup. Hence, further fracture resistance studies can be undertaken in carious teeth than in intact teeth to assess the efficacy in real-time.

It has been reported that CBCT images have higher reliability and validity than intraoral radiographic techniques in managing an endodontic diagnosis and its complications. Hence, its application in the evaluation of fracture strength of teeth is highly accepted.

   Conclusion Top

Compared to the traditional access cavity design, conservative designs including CEC, DDC, and NEC have improved fracture resistance. Compression load fractures are generally unrestorable in endodontically treated teeth irrespective of the designs. CBCT can be an ideal alternative in the diagnosis and treatment in the field of endodontics. The usefulness of CBCT imaging can no longer be disputed, CBCT is a useful task-specific imaging modality and an important technology in comprehensive endodontic evaluation.

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Conflicts of interest

There are no conflicts of interest.

   References Top

Patel S, Rhodes J. A practical guide to endodontic access cavity preparation in molar teeth. Br Dent J 2007;203:133-40.  Back to cited text no. 1
Bóveda C, Kishen A. Contracted endodontic cavities: the foundation for less invasive alternatives in the management of apical periodontitis. Endod Topics 2015;33:169-86.  Back to cited text no. 2
Clark D, Khademi JA. Modern molar endodontic access and directed dentin conservation. Dent Clin North Am 2010;54:249-73.  Back to cited text no. 3
Clark D, Khademi JA. Case studies in modern molar endodontic access and directed dentin conservation. Dent Clin North Am 2010;54:275-89.  Back to cited text no. 4
Auswin MK, Ramesh S. Truss access new conservative approach on access opening of a lower molar: A case report. J Adv Pharm Edu Res 2017;7:344-7.  Back to cited text no. 5
Plotino G, Grande NM, Isufi A, Ioppolo P, Pedullà E, Bedini R, et al. Fracture strength of endodontically treated teeth with different access cavity designs. J Endod 2017;43:995-1000.  Back to cited text no. 6
Gluskin AH, Peters CI, Peters OA. Minimally invasive endodontics: Challenging prevailing paradigms. Br Dent J 2014;216:347-53.  Back to cited text no. 7
Bóveda C. Clinical impact of cone beam computed tomography in root canal treatment. Endodontic Radiology. 2nd ed. Iowa: Wiley-Blackwell; 2012. p. 367-415.  Back to cited text no. 8
Patel S, Durack C, Abella F, Roig M, Shemesh H, Lambrechts P, et al. European Society of endodontology position statement: The use of CBCT in endodontics. Int Endod J 2014;47:502-4.  Back to cited text no. 9
Ikram OH, Patel S, Sauro S, Mannocci F. Micro-computed tomography of tooth tissue volume changes following endodontic procedures and post space preparation. Int Endod J 2009;42:1071-6.  Back to cited text no. 10
Özel Bektas Ö, Eren D, Herguner Siso S, Akin GE. Effect of thermocycling on the bond strength of composite resin to bur and laser treated composite resin. Lasers Med Sci 2012;27:723-8.  Back to cited text no. 11
Özyürek T, Ülker Ö, Demiryürek EÖ, Yılmaz F. The effects of endodontic access cavity preparation design on the fracture strength of endodontically treated teeth: Traditional versus conservative preparation. J Endod 2018;44:800-5.  Back to cited text no. 12
Mookhtia H, Hegde V, Srilatha S, Chopra M. Conservative endodontics: A truss access case series. Indian J Appl Dent Sci 2019;5:213-8.  Back to cited text no. 13
Lin CY, Lin D, He WH. Impacts of 3 different endodontic access cavity designs on dentin removal and point of entry in 3-dimensional digital models. J Endod 2020;46:524-30.  Back to cited text no. 14
Krishan R, Paqué F, Ossareh A, Kishen A, Dao T, Friedman S. Impacts of the conservative endodontic cavity on root canal instrumentation efficacy and resistance to fracture assessed in incisors, premolars, and molars. J Endod 2014;40:1160-6.  Back to cited text no. 15
Moore B, Verdelis K, Kishen A, Dao T, Friedman S. Impacts of contracted endodontic cavities on instrumentation efficacy and biomechanical responses in maxillary molars. J Endod 2016;42:1779-83.  Back to cited text no. 16
Segarra MS, Shimada Y, Sadr A, Sumi Y, Tagami J. Three-dimensional analysis of enamel crack behavior using optical coherence tomography. J Dent Res 2017;96:308-14.  Back to cited text no. 17
Al Amri MD, Al-Johany S, Sherfudhin H, Al Shammari B, Al Mohefer S, Al Saloum M, et al. Fracture resistance of endodontically treated mandibular first molars with conservative access cavity and different restorative techniques: An in vitro study. Aust Endod J 2016;42:124-31.  Back to cited text no. 18
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Bassir MM, Labibzadeh A, Mollaverdi F. The effect of the amount of lost tooth structure and restorative technique on fracture resistance of endodontically treated premolars. J Conserv Dent 2013;16:413-7.  Back to cited text no. 20
[PUBMED]  [Full text]  
Pradeep PR, Kumar VC, Bantwal SR, Gulati GS. Fracture strength of endodontically treated premolars: An In-vitro evaluation. J Int Oral Health 2013;5:9-17.  Back to cited text no. 21


  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2]


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